Most scholars agree that grammatical borrowing is a serious obstacle to syntactic reconstruction, but to date there have been few proposed solutions to this methodological conundrum. In this paper I propose a method, couched in a constructional view of language, for mitigating the problem of borrowing in syntactic reconstruction. The method begins with the reconstruction of partially schematic constructions, whose phonological material can be tested for cognacy. Fully schematic reconstructions are then achieved via generalizations made over sets of reconstructed constructions. I exemplify the effectiveness of this method by applying it to two pieces of grammar from the Sogeram languages of Papua New Guinea: clause chain nominalization and the desiderative construction. The method allows the reconstruction of the former, but identifies the latter as a likely grammatical borrowing and therefore not reconstructable to Proto-Sogeram.